1. Field of the Invention
The present invention relates in general to light metal cylinder heads for internal combustion engines and more particularly to valve seat inserts thereof.
2. Description of the Prior Art
Valve seat inserts are widely used in current automobile engines having light metal or aluminum alloy cylinder heads.
FIG. 1 shows a prior art aluminum alloy cylinder head 10 having a cast, aluminum alloy block 12 with a water jacket 14. The block 12 has a hole 16 prepared by machining at an end of an intake or exhaust port 18. A valve seat insert 20 made of hard, heat-resisting metal is inserted into the hole 16 and held in place by interference fit. After insertion, the valve seating surface of the valve seat insert 20 is ground in a manner as to be aligned with a valve guide 22.
The prior art light metal cylinder head of the above described type encounters the following drawbacks. That is, it is of great importance for the valve seat insert 20 to fit tightly all around the hole 16 in order to provide efficient heat transfer from the valve seat insert 20 to the block 12. This, however, necessitates hightly accurate machining of the valve seat insert 20 and the hole 16 and therefore results in an expensive manufacturing cost. Further, the pressed-in insert 20 requires a wall portion 24 of the block 12 surrounding the hole 16 to be thick enough to have sufficient strength. This results in poor heat transfer from the valve seat insert 20 to the water jacket 14.